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Drive and Controls Systems for Lift Trucks
The Right Drive for Hard Terrain
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Off-road lift trucks are characterised by high ground clearance, off-road tyres and – in some vehicles – an optional differential lock. Economy, manoeuvrability and high performance are also in the foreground. Traditionally, off-road lift trucks have rear-wheel drive, while some manufacturers also produce machines with centre-pivot steering. All requirements and tasks demanded of the hydraulic system in off-road lift trucks can be amply satisfied in an optimum fashion by the Rexroth product range. For example, we offer hydrostatic drives that are designed for different bearing forces and are equipped with the corresponding drives for mastering these forces.
Hydrostatic drive
The task of the hydrostatic drive for off-road lift trucks is, above all, to prevent the wheels spinning and thereby a loss of traction during off-road operation. To this aim, Rexroth offers either the axle drive with axial piston motor or the single-wheel drive with wheel gearbox.
Axle drive with axial piston motor
The standardised drive consists of a variable displacement pump and an actuating motor which is flange-mounted directly to a ring and pinion. A mechanical differential lock prevents the wheels from spinning on uneven and slippery ground. Traction is maintained one hundred percent. The drive can be either hydraulically or electronically controlled.
Single-wheel drive with wheel gearbox
In vehicle designs in which axle drive is impossible, the single-wheel drive with actuating motors and an electronic anti-slip control provides the solution for off-road operation. Here, two wheel gearboxes each with a flange-mounted axial piston motor are employed. The electronic control unit monitors the motor revolutions and compensates them if they deviate too far from setpoints. In this way, impaired traction is prevented.
Systems for working hydraulics
Two types of system are available for the working hydraulics of off-road lift trucks: open centre systems with gear pumps and load sensing systems with constant or variable displacement pumps.
Open centre system
Open centre systems with gear pumps are well-proven and robust, and impress through their compact, sturdy construction. The directional control valves can be mechanically, hydraulically or electrohydraulically operated and, additionally, offer a multitude of possibilities when it comes to combination.
Load sensing system
In load sensing systems with variable displacement pump, oil is supplied to the system – comprising a brake, steering system and control block – by a pump. The quantity supplied by the pump varies with the changing demand as a result of the LS signal fed back to the pump. At the same time, a priority valve ensures that the brake and steering system have priority. Advantages of this system are the demand-oriented supply to consumers and the load-independent flow distribution. Sensitive operation, electric actuation via CAN bus and an extremely good thermal characteristic are further benefits of this system.
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